The present invention relates to mine roof expansion anchors of the type having a radially expansible shell and a tapered plug moveable axially within the shell to effect expansion thereof. More specifically, the invention relates to novel structures of mine roof expansion anchors and tapered plug elements thereof for installation together with a resin grouting mix in a drill hole in a mine roof, or the like, and to methods of installation of combined resin-mechanical anchors.
For many years, one of the most popular means of providing support and reinforcement to mine roofs and other subterranean structures has been the mechanical expansion anchor. Such anchors have been proposed in a wide variety of designs having in common a radially expansible shell portion and a tapered plug having an internally threaded, axial bore. The threaded end of a bolt or other elongated rod is engaged with the bore of the tapered plug and the shell is suitably supported in surrounding relation to the smaller end of the plug. The end of the rod carrying the anchor is inserted into a pre-drilled hole in the rock structure, and the shell is expanded into tight engagement with the drill hole wall by rotation of the bolt to move the larger portion of the plug into the shell.
More recently, the effectiveness and useful life of anchorages have been enhanced by the use of quick-setting resin grouting mixes conjointly with mechanical anchors. Such mixes are commercially available in elongated, breakable tubes or cartridges having a diameter approximating that of the drill hole, and separate compartments containing a resin and a catalyst which are in a flowable condition prior to mixing. The lengths of the resin cartridge and bolt are so related to the depth of the drill hole that forced insertion of the bolt crushes the cartridge against the end of the drill hole, releasing the two components which are mixed to the extent necessary as they pass through and around the anchor and end of the bolt, and by rotation of the bolt to move the plug axially into the shell. Upon mixing of the components, the grouting mix hardens in a few seconds.
Since the resin cartridge is positioned between the blind end of the drill hole and the upper end of the expansion anchor, the components of the grouting mix must flow around and/or through the anchor components when the cartridge is broken. Ideally, the cured grouting mix should surround at least those portions of the anchor components not in direct, compressive engagement with the drill hole wall, as well as the upper portion of the bolt, usually to a position somewhat below the lower end of the anchor. Expansion anchors disclosed in a number of U.S. patents, including U.S. Pat. Nos. 4,859,118, 4,969,778 and 5,009,549, provide resin flow passages in the form of axial grooves in the tapered plug between the surfaces thereof which engage the inner surfaces of the shell. In the anchor of applicant's U.S. Pat. No. 5,316,414, resin flow passages are provided by axial grooves in the opposing wedge and/or shell surfaces.
It is a principal object of the present invention to provide a mine roof expansion anchor having novel and improved means for flow of resin mix components around and through the shell.
Another object is to provide an improved expansion shell for a mine roof anchor which enhances performance of the anchor, particularly when used with a resin grouting mix.
A further object is to provide an expansion shell with uniquely positioned resin flow passages for use in combined resin-mechanical anchorages for rock structure supports.
Still another object is to provide a novel method of anchoring the distal end of a mine roof bolt in a drill hole using both a mechanical anchor and resin to achieve enhanced performance.
Other objects will in part be obvious and will in part appear hereinafter.